Command line timewarp syntax

[andchir]

Describe the bug
Please tell me the correct syntax for timewarp in the command line. I did this, but got incorrect results.

To Reproduce
Before (without timewarp):

/usr/bin/melt \
-progress progressive=1 frame_rate_num=25 display_aspect_num=16 display_aspect_den=9 \
-track  \
"/home/andrew/Video/Original English Video.mp4" in=0 out=47 \
"/home/andrew/Video/Original English Video.mp4" in=48 out=100 \
"/home/andrew/Video/Original English Video.mp4" in=101 out=160 \
-profile atsc_1080p_25 \
-consumer avformat:"/home/andrew/Video/out.mp4" \
vcodec=libx264 vb=4096000 minrate=4096000 maxrate=4096000 acodec=aac ab=128k frequency=44100 deinterlace=1

After (timewarp):

/usr/bin/melt \
-progress progressive=1 frame_rate_num=25 display_aspect_num=16 display_aspect_den=9 \
-track  \
"/home/andrew/Video/Original English Video.mp4" in=0 out=47 \
timewarp:0.5:"/home/andrew/Video/Original English Video.mp4" warp_pitch=1 in=48 out=152 \
"/home/andrew/Video/Original English Video.mp4" in=101 out=160 \
-profile atsc_1080p_25 \
-consumer avformat:"/home/andrew/Video/out2.mp4" \
vcodec=libx264 vb=4096000 minrate=4096000 maxrate=4096000 acodec=aac ab=128k frequency=44100 deinterlace=1

If I understand correctly, I should increase the duration of the clip by 2 times, that is, change the value of the "out" parameter.
But I get a weird video freeze.

Results:

out.mp4

out2.mp4

CMD Melt:

• OS: Ubuntu
• OS Version 26
• melt 7.36.1

[ddennedy]

You may need to also increase the length property. That is the duration of the source. If you try to make an out value greater than length, it is simply truncated to length. Run melt -profile atsc_1080p_25 -consumer xml "/home/andrew/Video/Original English Video.mp4" to get the length for 25 fps from the XML output.

[andchir]

@ddennedy

Thank you for your reply!
Is this correct syntax? Should I increase the full clip length?

/usr/bin/melt \
-progress progressive=1 frame_rate_num=25 display_aspect_num=16 display_aspect_den=9 \
-track  \
"/home/andrew/Video/Original English Video.mp4" length=258 in=0 out=39 \
"/home/andrew/Video/Original English Video.mp4" length=258 in=40 out=100 \
timewarp:0.5:"/home/andrew/Video/Original English Video.mp4" warp_pitch=1 length=516 in=40 out=160 \
-profile atsc_1080p_25 \
-consumer avformat:"/home/andrew/out2.mp4" \
vcodec=libx264 vb=4096000 minrate=4096000 maxrate=4096000 acodec=aac ab=128k frequency=44100 deinterlace=1

But I still get an incorrect result.

out2.mp4

[andchir]

/usr/bin/melt \
-progress progressive=1 frame_rate_num=25 display_aspect_num=16 display_aspect_den=9 \
-track  \
"/home/andrew/Video/Original English Video.mp4" length=70 in=40 \
timewarp:0.5:"/home/andrew/Video/Original English Video.mp4" warp_pitch=1 length=140 in=40 \
-profile atsc_1080p_25 \
-consumer avformat:"/home/andrew/out2.mp4" \
vcodec=libx264 vb=4096000 minrate=4096000 maxrate=4096000 acodec=aac ab=128k frequency=44100 deinterlace=1

I get the correct result if I don't use the "out" parameter.

out2.mp4

[bmatherly]

My expectation is that you would need to multiply the "in" parameter to create frame continuity. When you make a timewarp with 0.5 speed, each frame is doubled. So, what was frame 40 at normal speed is now frame 80 at half speed. The same comment goes for "out" and "length".

I think an easy way to calculate it would be to calculate the frames you want for each segment. Then, for the timewarp producer, double the in and out values.

I do not think you would need to set length. But i did not test it myself.

[andchir]

@bmatherly
Thanks for your reply. However, I couldn't get the "out" parameter to work for timewarp. I also don't quite understand the logic involved. When the timewarp is 0.5, I don't need to change the "in" parameter value (as seen in the result above). But if the timewarp is 0.7, I have to multiply the original "in" value by 0.7. Could someone explain the logic here?

/usr/bin/melt \
-progress progressive=1 frame_rate_num=25 display_aspect_num=16 display_aspect_den=9 \
-track  \
"/home/andrew/Video/Original English Video.mp4" in=0 out=39 \
timewarp:0,7:"/home/andrew/Video/Original English Video.mp4" warp_pitch=1 length=100 in=28 \
"/home/andrew/Video/Original English Video.mp4" in=40 out=110 \
-profile atsc_1080p_25 \
-consumer avformat:"/home/andrew/Video/out_07.mp4" \
vcodec=libx264 vb=4096000 minrate=4096000 maxrate=4096000 acodec=aac ab=128k frequency=44100 deinterlace=1

Result

out_07.mp4

[andchir]

Here is my original video for testing.

Original.English.Video.mp4

[andchir]

To increase the speed of the specific section, I need to multiply the initial "in" parameter by 0.25 (40 * 0.25 = 10).

/usr/bin/melt \
-progress progressive=1 frame_rate_num=25 display_aspect_num=16 display_aspect_den=9 \
-track  \
"/home/andrew/Video/Original English Video.mp4" in=0 out=39 \
timewarp:2.0:"/home/andrew/Video/Original English Video.mp4" warp_pitch=1 in=10 length=35 \
"/home/andrew/Video/Original English Video.mp4" in=40 out=110 \
-profile atsc_1080p_25 \
-consumer avformat:"/home/andrew/Video/out_2.mp4" \
vcodec=libx264 vb=4096000 minrate=4096000 maxrate=4096000 acodec=aac ab=128k frequency=44100 deinterlace=1

out_2.mp4

[bmatherly]

To increase the speed of the specific section, I need to multiply the initial "in" parameter by 0.25 (40 * 0.25 = 10).

I have been doing some testing and I see the same problem. When I try to recreate this problem in Shotcut, the in/out math follows my previous instruction (double them for 0.5 speed). But it does not work in melt. There must be some interaction that I have not figured out yet that is causing melt to have incorrect behavior.

I do not know your full use case, but have you considered using the timeremap link instead of snipping up the clip?
https://www.mltframework.org/plugins/LinkTimeremap/

This link was designed to make keyframed speed adjustments to clips.

A good way to learn is to open your clip in Shotcut, apply the "Time Remap" or "Speed: Forward" filters (both use timeremap under the hood) and then apply keyframes to get the effect you want. Then, inspect the resulting MLT fil to see the parameters that are used.